1. Field of the Invention
This invention relates to a hybrid electric vehicle comprising an internal combustion engine, charging system, batteries and electric motor and, more particularly, to a hybrid vehicle temperature control system utilizing heat from the internal combustion engine to maintain the batteries within a predetermined temperature range for enhanced storage capacity and extended battery life, within a variety of climatic and operating conditions.
2. Description of the Related Art
Pure electric vehicles use batteries as the sole energy supply for all of the vehicle""s functions, at all times. This includes supplying heat for passengers in cold weather. Although batteries supply clean energy, their storage capacity is limited. The additional drain of providing heat to the passenger compartment further reduces range and performance. This problem is exacerbated by the effect of cold on batteriesxe2x80x94low temperatures diminish their available energy. If low enough, cold will deaden and damage the batteries.
Internal combustion engines, unlike electric motors, easily produce large amounts of power without requiring massive energy storage devices such as batteries. This is well-known, as evidenced by the large number of internal combustion vehicles on the road today. An equally well known fact is that internal combustion engines are polluting, as anyone can witness the smog problem continuing to plague cities and their suburbs. Further, the news reports of pollution from developing countries, with large numbers of people turning to automobiles for conveyance, are increasing. Linked to their pollution problem is that internal combustion engines are inefficient, as they waste most of the fuel energy as heat. More than half of the available energy in gasoline is lost as heat from the exhaust pipe and radiator. Adding to the inefficiency is that internal combustion engines, due to their power versus engine speed characteristics require speed reduction units. e.g., transmissions, to utilize their output. The typical transmission in the average car on the road today weight several hundred pounds. Still another shortcoming with internal combustion engines is that they are not efficient before reaching their optimum operating temperature. Therefore, the typical driver has two choices; one is to warm the engine up until it reaches that temperature, which wastes fuel, and the other is to drive off immediately, which wastes fuel as well, in addition to hastening engine wear.
Electric vehicles have been considered as a solution to the environmental problems of internal combustion engines. However, there are multiple problems, some of which have been identified above, which combine to make electric vehicles impractical for most applications today. Vehicle range is a major problem. Batteries do not have enough storage capacity in terms of amp-hours per pound or per cubic foot. Batteries are expensive. Therefore, if a vehicle is designed to have a load capacity comparable to one having an internal combustion engine, and have acceptable speed and acceleration, and yet be affordable, the range is limited to about a hundred miles. Increasing the range, for example, to two hundred miles would require approximately twice the battery capacity. It is well known in the art that, in view of the large amount of vehicle volume already filled with batteries, together with their weight and cost, that such an increase might render the vehicle impractical.
The problems of high battery cost, in terms of purchase price and vehicle weight, and limited range imposed by that cost is severely exacerbated by cold climate. A major cause of this climate-induced problem is that the capacity of lead-acid batteries diminishes as the temperature goes down. For example, a conventional lead-acid battery in a standard automobile which is typically rated at 200 ampere hours when new, will test at approximately one half that value when the battery is chilled down to 20 degrees Fahrenheit. This problem is generally tolerable for internal combustion cars, because the battery has enough excess capacity, until it ages approximately three years, to operate the starter motor, even when half of its reserve is gone due to the cold weather. However, the present inventor has recognized that the deleterious effects of cold weather on the batteries of electric vehicles require a new method and apparatus.
Yet another problem is that batteries generate heat when subjected to the drain and recharge rates required for electric vehicles. This problem is of particular concern if the vehicle will be subjected to high-demand driving, such as hard acceleration, sustained high speeds, and climbing grades. The heat build-up can significantly reduce the life of the battery. Because these driving conditions are unavoidable, compensation must be made, including reducing the vehicle""s design speed and reducing its acceleration, which in turn reduces the maximum rate of discharge. These solutions however, decrease the practicality, safety, and appeal of an electric vehicle.
There are other issues pertaining to battery temperature that affect its peak current discharge, storage capacity and life. More particularly, several battery types deliver maximum output at higher temperatures, because their energy is stored in a chemical reaction which is temperature dependent. Lowering the temperature suppresses the activity of the reaction, and raising the temperature (within the limitation of the batteries"" tolerance) increases the available output.
For example, the practical output of power for lead-acid batteries is highest at about 43 degrees C. (110 degrees F.)xe2x80x94roughly double the output of the same battery below 0 degrees C. Similarly, optimal temperatures for nickel-cadmium and metal hydride batteries are approximately 30 degrees C. (86 degrees F.) and 45 degrees C. (113 degrees F.), respectively. Sodium-nickel batteries will not function at all below 200 degrees C.
The result is that even on a hot summer day, the full output of many battery types is not available. In cold months, it becomes fractional.
Hybrid vehicles have been identified as a partial solution to the above-identified problems. A hybrid vehicle is obtained by installing a small internal combustion engine and alternator or generator into an electric vehicle. The immediate improvement over a pure electric vehicle is that the batteries can be charged while the vehicle is moving, and thus the range can be increased over what is possible with stationary charging. In addition, the internal combustion engine and generator can provide added current to the electric motor during heavy load or high-demand acceleration conditions. However, the internal combustion engine reintroduces the pollution and fuel consumption problems which the electric vehicle was directed to solving. In addition, the inefficiencies of the internal combustion engine, in terms of the percentage of available energy of the fuel that is converted into motion of the vehicle, is exacerbated when used in a hybrid vehicle. The reason is that generators are, at best, about 75% efficient, meaning that 25% of the power driving the generator is converted into heat, instead of into electric current.
Therefore, a need exists for improving the battery storage capacity of a hybrid vehicle such that its internal combustion engine can be substantially smaller than that required by prior art hybrid vehicles, without any sacrifice in performance or increased cost.
These and other objectives are achieved by the present invention""s novel feature of transferring heat from the internal combustion engine of a hybrid vehicle to the vehicle""s batteries, in a controlled manner, to quickly bring the batteries up to their optimal operating temperature, and maintain them at that temperature, regardless of variations in operating conditions and environment.
A first embodiment comprises a small internal combustion engine, large enough to produce adequate heat for warming the passenger compartment, drives an alternator or generator. Hot coolant from the engine passes through a radiator which also serves as the passenger heater. Coolant from the radiator/heater then circulates through a regulated flow heat exchanger system, having structure thermally conductive with the batteries, for regulating battery temperature. The coolant, after being heat-depleted by circulation through the battery exchanger system, flows to a second exchanger in contact with heat recovered from the engine exhaust and catalytic converter gases. Heat energy absorbed from the exhaust exchanger reheats the coolant to a temperature, set by thermostatically regulated flow through the exhaust exchanger, which is for optimal operating efficiency of the engine, and then returns to the engine block.
Once the batteries have reached their pre-determined operating temperature, the internal combustion engine of the hybrid system may be shut off. The vehicle can then operate as a pure electric vehicle. The internal combustion engine is restarted if passenger heat is needed or if the battery temperature becomes too low.
An alternator driven by the internal combustion engine supplies electrical current for auxiliary power and recharging the batteries. When the vehicle is stationary, as at a stop-light or traffic jam, the system can continue charging the batteries. In urban driving conditions, this self-generated power can extend the range of the vehicle, and provide current to compensate for the drain of night-time lighting.
During warm weather, passenger heat is not needed, and the internal combustion engine of the hybrid system can be shut off once the batteries are at optimal temperature. Operation of the system can be resumed to meet high-demand driving situations, or when driving the vehicle near the limit of its charge range, or in a low state of charge. When the hybrid system is in operation, and the vehicle driven in rapid discharge situations, the system allows some of the resulting excess heat to be removed through the regulatory components using an external exchanger. This function protects the batteries from damage and increases their life. When the vehicle is not in use, it can be charged from an electrical outlet, just as a pure electric vehicle would.
A further embodiment of the invention comprises, in combination with the first embodiment, a plurality of flow tubes disposed with one or more of the batteries, to provide a flow path for the heat exchanger fluid through said one or more batteries.
A still further embodiment comprises, in combination with either of the above-summarized embodiments, a radiator formed integral with one or more of the external body panels of the automobile.